X-chromosome inactivation in the Wiskott-Aldrich syndrome: a marker for detection of the carrier state and identification of cell lineages expressing the gene defect

Síndrome de Wiskott-Aldrich en España: incidencia, mortalidad y sesgo de género durante 21 años

Antecedentes

El síndrome de Wiskott-Aldrich (SWA) es un raro trastorno ligado al cromosoma X que se considera que afecta predominantemente a varones.

Objetivo

El objetivo de este estudio consistía en investigar la incidencia y la mortalidad intrahospitalaria del SWA en España, así como el sesgo de género.

Métodos

Se llevó a cabo un estudio epidemiológico retrospectivo poblacional en 97 pacientes con SWA diagnosticados en hospitales españoles entre 1997 y 2017, utilizando para ello datos del Sistema Nacional de Vigilancia de Datos Hospitalarios.

Resultados

Nuestros resultados revelaron que la incidencia anual media del SAW en España fue de 1,1 caso por cada 10 millones de habitantes (IC del 95 %, 0,45-2,33). El riesgo relativo fue mayor en los varones que en las mujeres (2,42). El diagnóstico de SWA se establece a una edad más avanzada en las mujeres (mediana de 47 años) que en los varones (mediana de 5,5 años). Únicamente los varones ingresaron en el hospital en al menos 10 ocasiones diferentes y todas las muertes se detectaron en varones. La tasa de mortalidad intrahospitalaria fue del 9,28 % en el SAW y la mayoría de las muertes se asociaron a hemorragia cerebral o infección.

Conclusiones

El SWA, una enfermedad rara, se diagnostica a una edad más avanzada en las mujeres y la mortalidad se observó exclusivamente en varones, asociada en la mayoría de los casos a hemorragia cerebral e infección.

Understanding immunoactinopathies: A decade of research on WAS gene defects

Immunoactinopathies caused by mutations in actin-related proteins are a growing group of inborn errors of immunity (IEI). Immunoactinopathies are caused by a dysregulated actin cytoskeleton and affect hematopoietic cells especially because of their unique capacity to survey the body for invading pathogens and altered self, such as cancer cells. These cell motility and cell-to-cell interaction properties depend on the dynamic nature of the actin cytoskeleton. Wiskott-Aldrich syndrome (WAS) is the archetypical immunoactinopathy and the first described. WAS is caused by loss-of-function and gain-of-function mutations in the actin regulator WASp, uniquely expressed in hematopoietic cells. Mutations in WAS cause a profound disturbance of actin cytoskeleton regulation of hematopoietic cells. Studies during the last 10 years have shed light on the specific effects on different hematopoietic cells, revealing that they are not affected equally by mutations in the WAS gene. Moreover, the mechanistic understanding of how WASp controls nuclear and cytoplasmatic activities may help to find therapeutic alternatives according to the site of the mutation and clinical phenotypes. In this review, we summarize recent findings that have added to the complexity and increased our understanding of WAS-related diseases and immunoactinopathies.

Wiskott Aldrich syndrome: healthcare utilizations and disparities in transplant care

Wiskott Aldrich syndrome (WAS) is a rare disease and hematopoietic stem cell transplant (HCT) is considered the treatment modality of choice for WAS. We conducted a cross-sectional analysis on the KIDS' pediatric inpatient database and compared hospitalization rates, complications and healthcare utilizations in the transplant and non-transplant arms. Of the 383 pediatric admissions with diagnosis of WAS between 2006-2012, 114 underwent transplant and 269 did not. The non-transplant arm included older children, female patients and more African Americans. Death rates, income and payer source were similar in both arms, however the total charge for each admission was higher in the transplant arm. Emergency room visits were similar but non-elective admissions were more in the non-transplant arm. Length of stay was prolonged in the transplant arm. When comparing morbidities, lymphomas, ulcerative colitis and autoimmune complications of WAS were seen only in the non-transplant arm. Our study shows that transplant is the largest contributor to healthcare utilization in WAS patients. We identified healthcare disparities based on race and socioeconomic status and found that this rare disease is being appropriately directed to centers with HCT expertise. We noted a change in practice moving away from splenectomy in WAS patients.

A new sex-specific underlying mechanism for female schizophrenia: accelerated skewed X chromosome inactivation

BACKGROUND

X chromosome inactivation (XCI) is the mechanism by which the X-linked gene dosage is adjusted between the sexes. Evidence shows that many sex-specific diseases have their basis in X chromosome biology. While female schizophrenia patients often have a delayed age of disease onset and clinical phenotypes that are different from those of males, it is unknown whether the sex differences in schizophrenia are associated with X-linked gene dosage and the choice of X chromosome silencing in female cells. Previous studies demonstrated that sex chromosome aneuploidies may be related to the pathogeneses of some psychiatric diseases. Here, we examined the changes in skewed XCI in patients with schizophrenia.

METHODS

A total of 109 female schizophrenia (SCZ) patients and 80 age- and sex-matched healthy controls (CNTLs) were included in this study. We evaluated clinical features including disease onset age, disease duration, clinical symptoms by the Positive and Negative Syndrome Scale (PANSS) and antipsychotic treatment dosages. The XCI skewing patterns were analyzed by the methylation profile of the HUMARA gene found in DNA isolated from SCZ patient and CNTL leukocytes in the three age groups.

RESULTS

First, we found that the frequency of skewed XCI in SCZ patients was 4 times more than that in the age- and sex-matched CNTLs (p < 0.01). Second, we found an earlier onset of severe XCI skewing in the SCZ patients than in CNTLs. Third, we demonstrated a close relationship between the severity of skewed XCI and schizophrenic symptoms (PANSS score ≥ 90) as well as the age of disease onset. Fourth, we demonstrated that the skewed XCI in SCZ patients was not transmitted from the patients' mothers.

LIMITATIONS

The XCI skewing pattern might differ depending on tissues or organs. Although this is the first study to explore skewed XCI in SCZ, in the future, samples from different tissues or cells in SCZ patients might be important for understanding the impact of skewed XCI in this disease.

CONCLUSION

Our study, for the first time, investigated skewed XCI in female SCZ patients and presented a potential mechanism for the sex differences in SCZ. Our data also suggested that XCI might be a potential target for the development of female-specific interventions for SCZ.

Exome sequence identified a c.320A > G ALG13 variant in a female with infantile epileptic encephalopathy with normal glycosylation and random X inactivation: Review of the literature

Congenital Disorders of Glycosylation (CDG) are new and rapidly expanding neurometabolic disorders with multisystem involvements, broad phenotypic manifestations, and variable severity. The majority results from a defect of one of the steps involved with protein or lipid N-glycosylation pathway. Almost all are inherited in autosomal recessive patterns with a few exceptions such as the X-linked ALG13. Mutations of ALG13 are reported, so far in only 10 patients, all were ascertained through exome/genome sequencing. Specifically, the ALG13 c.320A > G (p.Asn107Ser) variant was reported only in females and in all were de novo mutations. These findings may suggest an X-linked dominant inheritance of this mutation with embryonic male lethality. These patients presented with severe infantile epileptic encephalopathy, global developmental delay, and multisystem abnormalities. Only two of these females had glycosylation studies done, and both showed normal pattern of glycosylated serum transferrin isoforms, and none had their X-chromosome inactivation patterns studied. Here, we report on another female patient who is heterozygous for the same ALG13 c.320A > G (p.Asn107Ser) variant. She presented with infantile spasms, epileptic encephalopathy, hypsarrhythmia, hypotonia, developmental delay, intellectual disability, abnormal coagulation profile, feeding problems, hypotonia, and dysmorphic features. The diagnosis of CGD was suspected clinically, but glycosylation studies were done twice and showed normal patterns on both occasions. Her X-inactivation study was also done and, surprisingly, showed a random pattern of X-inactivation, with no evidence of skewness.

Actin cytoskeletal defects in immunodeficiency

The importance of the cytoskeleton in mounting a successful immune response is evident from the wide range of defects that occur in actin-related primary immunodeficiencies (PIDs). Studies of these PIDs have revealed a pivotal role for the actin cytoskeleton in almost all stages of immune system function, from hematopoiesis and immune cell development, through to recruitment, migration, intercellular and intracellular signaling, and activation of both innate and adaptive immune responses. The major focus of this review is the immune defects that result from mutations in the Wiskott-Aldrich syndrome gene (WAS), which have a broad impact on many different processes and give rise to clinically heterogeneous immunodeficiencies. We also discuss other related genetic defects and the possibility of identifying new genetic causes of cytoskeletal immunodeficiency.

Heritable skewed X-chromosome inactivation leads to haemophilia A expression in heterozygous females

Factor VIII gene, F8, mutations cause haemophilia A (HA), an X-linked recessive disorder. Expression in heterozygous females has been ascribed to skewed X-chromosome inactivation (XCI). To investigate the cause of HA in three heterozygous females within an Atlantic Canadian kindred, the proband (severely affected girl, FVIII activity: 2%) and 17 relatives across three generations were studied. F8 genotype, FVIII activity, XCI ratio (XCIR) (paternal active X: maternal active X), karyotype, submegabase resolution tiling set array competitive genome hybridization (competitive genomic hybridization (SMRT)), and microsatellite analyses were utilized. A positive linear relationship between FVIII activity and percentage-activated normal X-chromosome was found in HA heterozygous females (R(2)=0.87). All affected, but no unaffected females, had an XCIR skewed toward activation of the mutant X-chromosome (proband 92:8, SD 2). Unexpectedly, high numbers of females have dramatically skewed XCIRs (>80:20 or <20:80) (P<0.05). The distribution of XCIR frequencies within this family was significantly different than predicted by normal population data or models of random XCI (P<0.025), with more females having higher degrees of skewing. Known causes of skewing, such as chromosomal abnormalities, selection against deleterious alleles, and X-inactive-specific transcript mutations, are not consistent with our results. This study shows that FVIII activity in HA heterozygous females can be directly related to XCI skewing, and that low FVIII activity in females in this family is due to unfavourable XCI skewing. Further, the findings suggest that these XCI ratios are genetically influenced, consistent with a novel heritable human X controlling element (XCE) functioning similarly to the mouse Xce.

First among equals: competition between genetically identical cells

Competition between genetically identical organisms is considered insignificant in evolutionary theory because it is presumed to have little selective consequence. We argue that competition between genetically identical cells could improve the fitness of a multicellular organism by directing fitter cells to the germ line or by eliminating unfit cells, and that cell-competition mechanisms have been conserved in multicellular organisms. We propose that competition between genetically identical or highly similar units could have similar selective advantages at higher organizational levels, such as societies.

A novel splice site mutation in the WAS gene causes Wiskott–Aldrich syndrome in two siblings of a Saudi family

We report here on a Saudi family with two affected males with Wiskott-Aldrich syndrome (WAS), which includes mild to moderate bleeding and a low platelet count. A novel splice donor-site mutation (811 + 5 G <-- C) in intron 8 of the WAS gene (Genbank accession number NM_000377) was detected in a hemizygous status in both index cases, heterozygous in their mother and absent in the father. RNA from both index cases was transcribed and amplified with primers complementary to sequences in exons 7 and 10. A reverse transcription-polymerase chain reaction (RT-PCR) product of 688 bp (approximately 82%) was produced in addition to the normal RT-PCR product of 485 bp (approximately 18%). cDNA sequence analysis reveals an inclusion of full intron 8 sequence in the final transcript. The resultant protein is predicted to have 68 missense codons and a pre-mature stop codon at amino acid 260. This novel splice donor-site mutation was not detected in 80 normal controls (56 females and 24 males) from the same ethnic background as the index cases. Since no other mutation was detected in the WAS gene and the patients have classical symptoms of WAS, we concluded that it is highly likely that this novel mutation is responsible for the phenotype observed in these patients.

Wiskott–Aldrich syndrome in a female with skewed X-chromosome inactivation

Wiskott-Aldrich syndrome (WAS) is an X-linked recessive disorder characterized by immunodeficiency, eczema, and thrombocytopenia with small platelets. The phenotype of affected males is usually severe, although female carriers of the disorder have no clinical signs of the genetic defect. This is explained by the preferential selection of the normal, nonmutated X-chromosome, as the active allele in hematopoietic cells. In the present article we describe a female case of WAS, with a G-to-A transition in the WASP gene at nucleotide 291. She displays mild thrombocytopenia, with both normal and small-sized platelets. A methylation analysis of the HUMARA gene showed a nonrandom X-chromosome inactivation pattern in which the X-chromosome carrying the normal WASP gene was preferentially inactivated, leaving the mutant gene active. Thus, our results suggest that skewed X-inactivation, favoring the WASP-mutated allele, is the mechanism underlying the WAS phenotype of this girl. Moreover the results alert us to the fact that particular females, with a family history of WAS, may develop certain signs of the disease.

Second-site mutation in the Wiskott-Aldrich syndrome (WAS) protein gene causes somatic mosaicism in two WAS siblings

Revertant mosaicism due to true back mutations or second-site mutations has been identified in several inherited disorders. The occurrence of revertants is considered rare, and the underlying genetic mechanisms remain mostly unknown. Here we describe somatic mosaicism in two brothers affected with Wiskott-Aldrich syndrome (WAS). The original mutation causing disease in this family is a single base insertion (1305insG) in the WAS protein (WASP) gene, which results in frameshift and abrogates protein expression. Both patients, however, showed expression of WASP in a fraction of their T cells that were demonstrated to carry a second-site mutation causing the deletion of 19 nucleotides from nucleotide 1299 to 1316. This deletion abrogated the effects of the original mutation and restored the WASP reading frame. In vitro expression studies indicated that mutant protein encoded by the second-site mutation was expressed and functional, since it was able to bind to cellular partners and mediate T cell receptor/CD3 downregulation. These observations were consistent with evidence of in vivo selective advantage of WASP-expressing lymphocytes. Molecular analysis revealed that the sequence surrounding the deletion contained two 4-bp direct repeats and that a hairpin structure could be formed by five GC pairs within the deleted fragment. These findings strongly suggest that slipped mispairing was the cause of this second-site mutation and that selective accumulation of WASP-expressing T lymphocytes led to revertant mosaicism in these patients.

12. Primary immunodeficiency diseases

Although primary immunodeficiency disorders are relatively rare, intensive investigation of these disorders has yielded a great wealth of understanding of basic immunologic mechanisms in host defense, inflammation, and autoimmunity. These advances have led to important developments for the treatment not only of the primary immunodeficiencies but also for patients with secondary immunocompromised states, autoimmune disorders, hypersensitivity, graft rejection, and graft versus host disease. Correction of a form of severe combined immunodeficiency represents the first true success of human gene therapy. This review introduces the major clinical manifestations of primary immunodeficiency disorders, along with descriptions of essential elements of the pathophysiology of those disorders that have been defined at the molecular level. Key concepts in treatment are also presented. It is critical for the practicing primary care provider and allergist to maintain an index of suspicion for immunodeficiency. Early diagnosis offers the best opportunity for reduced morbidity and survival and is critical for accurate genetic counseling.

Wiskott-Aldrich syndrome in a female

Wiskott-Aldrich syndrome (WAS) is an X-linked disease characterized by thrombocytopenia, eczema, and various degrees of immune deficiency. Carriers of mutated WASP have nonrandom X chromosome inactivation in their blood cells and are disease-free. We report data on a 14-month-old girl with a history of WAS in her family who presented with thrombocytopenia, small platelets, and immunologic dysfunction. Sequencing of the WASP gene showed that the patient was heterozygous for the splice site mutation previously found in one of her relatives with WAS. Sequencing of all WASP exons revealed no other mutation. Levels of WASP in blood mononuclear cells were 60% of normal. Flow cytometry after intracellular staining of peripheral blood mononuclear cells with WASP monoclonal antibody revealed both WASP(bright) and WASP(dim) populations. X chromosome inactivation in the patient's blood cells was found to be random, demonstrating that both maternal and paternal active X chromosomes are present. These findings indicate that the female patient has a defect in the mechanisms that lead in disease-free WAS carriers to preferential survival/proliferation of cells bearing the active wild-type X chromosome. Whereas the patient's lymphocytes are skewed toward WASP(bright) cells, about 65% of her monocytes and the majority of her B cells (CD19(+)) are WASP(dim). Her naive T cells (CD3(+)CD45RA(+)) include WASP(bright) and WASP(dim) populations, but her memory T cells (CD3(+)CD45RA(-)) are all WASP(bright). After activation in vitro of T cells, all cells exhibited CD3(+)CD45RA(-) phenotype and most were WASP(bright) with active paternal (wild-type) X chromosome, suggesting selection against the mutated WASP allele during terminal T-cell maturation/differentiation.

Retrovirus-mediated WASP gene transfer corrects Wiskott-Aldrich syndrome T-cell dysfunction

The Wiskott-Aldrich syndrome (WAS) is an X-linked disorder characterized by thrombocytopenia, eczema, and immunodeficiency. At present, the only definitive therapy for the disease is allogeneic bone marrow transplantation (BMT). Because of the frequent lack of suitable donors and the potential severe complications associated with BMT, the development of gene-based therapeutic strategies for WAS is highly desirable. To study whether corrective gene transfer into WAS T cells can lead to restoration of the immunologic defects of WAS, a retroviral vector expressing the WAS protein (WASP) gene was used to transduce human T-lymphotropic virus type 1-transformed T-cell lines and primary T lymphocytes from patients with WAS. After transduction, WAS T cells showed levels of WASP expression similar to those found in cells from normal individuals. In addition, the reconstituted WASP interacted in vitro with proteins containing SH3 domain such as Grb2, PLC-gamma1, and Fyn, each of which are connected to signaling pathways linked to the actin cytoskeleton. Furthermore, after CD3 cross-linking, transduced WAS T lines showed improvement of actin polymerization and T-cell receptor/CD3 down-regulation. More importantly, primary WAS T lymphocytes transduced with WASP acquired the ability to proliferate in response to anti-CD3 stimulation. These findings suggest that biologic defects of WAS T cells can be corrected in vitro by retrovirus-mediated gene transfer and pose the basis for future investigation of gene therapy as treatment for WAS.

The role of X-chromosome inactivation in the manifestation of Rett syndrome

X-chromosome inactivation (XCI) is random in the majority of patients with classical Rett syndrome (RTT). Preferential inactivation of the X chromosome with the mutated MECP2 gene is found in mildly symptomatic or asymptomatic carrier females. These findings lead to a hypothesis that random XCI is causally involved in the pathogenesis of RTT in heterozygous females. It is the cluster of functionally defective nerve cells lacking fully functional MeCP2 generated by inactivation of normal MECP2 allele that causes the wide spectrum of RTT symptoms. Thus, RTT is a rare human disease manifestation which is triggered most probably by random XCI.

Somatic mosaicism in Wiskott--Aldrich syndrome suggests in vivo reversion by a DNA slippage mechanism

Somatic mosaicism caused by in vivo reversion of inherited mutations has been described in several human genetic disorders. Back mutations resulting in restoration of wild-type sequences and second-site mutations leading to compensatory changes have been shown in mosaic individuals. In most cases, however, the precise genetic mechanisms underlying the reversion events have remained unclear, except for the few instances where crossing over or gene conversion have been demonstrated. Here, we report a patient affected with Wiskott--Aldrich syndrome (WAS) caused by a 6-bp insertion (ACGAGG) in the WAS protein gene, which abrogates protein expression. Somatic mosaicism was documented in this patient whose majority of T lymphocytes expressed nearly normal levels of WAS protein. These lymphocytes were found to lack the deleterious mutation and showed a selective growth advantage in vivo. Analysis of the sequence surrounding the mutation site showed that the 6-bp insertion followed a tandem repeat of the same six nucleotides. These findings strongly suggest that DNA polymerase slippage was the cause of the original germ-line insertion mutation in this family and that the same mechanism was responsible for its deletion in one of the propositus T cell progenitors, thus leading to reversion mosaicism.

Mapping of a syndrome of X-linked thrombocytopenia with thalassemia to band Xp11-12: further evidence of genetic heterogeneity of X-linked thrombocytopenia

X-linked thrombocytopenia with thalassemia (XLTT; Online Mendelian Inheritance in Man [OMIM] accession number 314050) is a rare disorder characterized by thrombocytopenia, platelet dysfunction, splenomegaly, reticulocytosis, and unbalanced hemoglobin chain synthesis. In a 4-generation family, the gene responsible for XLTT was mapped to the X chromosome, short arm, bands 11-12 (band Xp11-12). The maximum lod score possible in this family, 2.39, was obtained for markers DXS8054 and DXS1003, at a recombination fraction of 0. Recombination events observed for XLTT and markers DXS8080 and DXS8023 or DXS991 define a critical region that is less than or equal to 7.65 KcM and contains the gene responsible for the Wiskott-Aldrich syndrome (WAS; OMIM accession number 301000) and its allelic variant X-linked thrombocytopenia (XLT; OMIM accession number 313900). Manifestations of WAS include thrombocytopenia, eczema, and immunodeficiency. In WAS/XLT the platelets are usually small, and bleeding is proportional to the degree of thrombocytopenia. In contrast, in XLTT the platelet morphology is normal, and the bleeding time is disproportionately prolonged. In this study no alteration in the WAS gene was detected by Northern blot or Western blot analysis, flow cytometry, or complimentary DNA dideoxynucleotide fingerprinting or sequencing. As has been reported for WAS and some cases of XLT, almost total inactivation of the XLTTgene-bearing X chromosome was observed in granulocytes and peripheral blood mononuclear cells from 1 asymptomatic obligate carrier. The XLTT carrier previously found to have an elevated :β hemoglobin chain ratio had a skewed, but not clonal, X-inactivation pattern favoring activity of the abnormal allele. Clinical differences and results of the mutation analyses make it very unlikely that XLTT is another allelic variant of WAS/XLT and strongly suggest that X-linked thrombocytopenia mapping to band Xp11-12 is a genetically heterogeneous disorder.

Mapping of a syndrome of X-linked thrombocytopenia with thalassemia to band Xp11-12: further evidence of genetic heterogeneity of X-linked thrombocytopenia

X-linked thrombocytopenia with thalassemia (XLTT; Online Mendelian Inheritance in Man [OMIM] accession number 314050) is a rare disorder characterized by thrombocytopenia, platelet dysfunction, splenomegaly, reticulocytosis, and unbalanced hemoglobin chain synthesis. In a 4-generation family, the gene responsible for XLTT was mapped to the X chromosome, short arm, bands 11-12 (band Xp11-12). The maximum lod score possible in this family, 2.39, was obtained for markers DXS8054 and DXS1003, at a recombination fraction of 0. Recombination events observed for XLTT and markers DXS8080 and DXS8023 or DXS991 define a critical region that is less than or equal to 7.65 KcM and contains the gene responsible for the Wiskott-Aldrich syndrome (WAS; OMIM accession number 301000) and its allelic variant X-linked thrombocytopenia (XLT; OMIM accession number 313900). Manifestations of WAS include thrombocytopenia, eczema, and immunodeficiency. In WAS/XLT the platelets are usually small, and bleeding is proportional to the degree of thrombocytopenia. In contrast, in XLTT the platelet morphology is normal, and the bleeding time is disproportionately prolonged. In this study no alteration in the WAS gene was detected by Northern blot or Western blot analysis, flow cytometry, or complimentary DNA dideoxynucleotide fingerprinting or sequencing. As has been reported for WAS and some cases of XLT, almost total inactivation of the XLTTgene-bearing X chromosome was observed in granulocytes and peripheral blood mononuclear cells from 1 asymptomatic obligate carrier. The XLTT carrier previously found to have an elevated :β hemoglobin chain ratio had a skewed, but not clonal, X-inactivation pattern favoring activity of the abnormal allele. Clinical differences and results of the mutation analyses make it very unlikely that XLTT is another allelic variant of WAS/XLT and strongly suggest that X-linked thrombocytopenia mapping to band Xp11-12 is a genetically heterogeneous disorder.

Antigen receptor-induced activation and cytoskeletal rearrangement are impaired in Wiskott-Aldrich syndrome protein-deficient lymphocytes

The Wiskott-Aldrich syndrome protein (WASp) has been implicated in modulation of lymphocyte activation and cytoskeletal reorganization. To address the mechanisms whereby WASp subserves such functions, we have examined WASp roles in lymphocyte development and activation using mice carrying a WAS null allele (WAS(-)(/)(-)). Enumeration of hemopoietic cells in these animals revealed total numbers of thymocytes, peripheral B and T lymphocytes, and platelets to be significantly diminished relative to wild-type mice. In the thymus, this abnormality was associated with impaired progression from the CD44(-)CD25(+) to the CD44(-)CD25(-) stage of differentiation. WASp-deficient thymocytes and T cells also exhibited impaired proliferation and interleukin (IL)-2 production in response to T cell antigen receptor (TCR) stimulation, but proliferated normally in response to phorbol ester/ionomycin. This defect in TCR signaling was associated with a reduction in TCR-evoked upregulation of the early activation marker CD69 and in TCR-triggered apoptosis. While induction of TCR-zeta, ZAP70, and total protein tyrosine phosphorylation as well as mitogen-activated protein kinase (MAPK) and stress-activated protein/c-Jun NH(2)-terminal kinase (SAPK/JNK) activation appeared normal in TCR-stimulated WAS(-)(/)(-) cells, TCR-evoked increases in intracellular calcium concentration were decreased in WASp-deficient relative to wild-type cells. WAS(-)(/)(-) lymphocytes also manifested a marked reduction in actin polymerization and both antigen receptor capping and endocytosis after TCR stimulation, whereas WAS(-)(/)(-) neutrophils exhibited reduced phagocytic activity. Together, these results provide evidence of roles for WASp in driving lymphocyte development, as well as in the translation of antigen receptor stimulation to proliferative or apoptotic responses, cytokine production, and cytoskeletal rearrangement. The data also reveal a role for WASp in modulating endocytosis and phagocytosis and, accordingly, suggest that the immune deficit conferred by WASp deficiency reflects the disruption of a broad range of cellular behaviors.

The Wiskott-Aldrich syndrome protein (WASP): roles in signaling and cytoskeletal organization

The Wiskott-Aldrich Syndrome (WAS) is a rare X-linked primary immunodeficiency that is characterized by recurrent infections, hematopoietic malignancies, eczema, and thrombocytopenia. A variety of hematopoietic cells are affected by the genetic defect, including lymphocytes, neutrophils, monocytes, and platelets. Early studies noted both signaling and cytoskeletal abnormalities in lymphocytes from WAS patients. Following the identification of WASP, the gene mutated in patients with this syndrome, and the more generally expressed WASP homologue N-WASP, studies have demonstrated that WASP-family molecules associate with numerous signaling molecules known to alter the actin cytoskeleton. WASP/N-WASP may depolymerize actin directly and/or serve as an adaptor or scaffold for these signaling molecules in a complex cascade that regulates the cytoskeleton.

Clonality Analysis of Benign Parathyroid Lesions by Human Androgen Receptor (HUMARA) Gene Assay

Benign conditions of the parathyroid gland have been classified as adenomas and hyperplasias. These entities however are difficult to distinguish when only a single gland is enlarged. Adenomas are defined as neoplastic clonal growths whereas hyperplasias are considered to be reactive processes of polyclonal origin. In order to analyze the clonal pattern of these lesions, we have studied hyperplasias and adenomas of parathyroid glands from women by the human androgen receptor (HUMARA) assay, a recently reliable and highly-lnformative technique based on the X-chromosome inactivation pattern in females. Samples consisted of formalin-fixed as well as frozen tissues. Informativeness with HUMARA marker was 87% (13/15 cases). All hyperplasias (5/5) and 6/8 adenomas yielded polyclonal results, since two alleles of similar intensity appeared when the lesion was HpaIl-digested. Two parathyroid adenomas had a loss of one X-alIeIe for the HUMARA gene and they were interpreted as monoclonal. These results show that parathyroid hyperplasias and adenomas, considered as multigland or monogland involvement diseases respectively, may be both polyclonal in origin, and that only a small subset of adenomas is found to be clonal. Consequently, clonality analysis cannot allow a clear distinction between these two entities as classically diagnosed. A different approach should be considering hyperplasia or adenoma when a polyclonal or monoclonal result has been obtained by clonality analysis.

A PCR-based non-radioactive X-chromosome inactivation assay for genetic counseling in X-linked primary immunodeficiencies

The Wiskott-Aldrich syndrome (WAS), X-linked severe combined immunodeficiency (SCIDX1), and X-linked agammaglobulinemia (XLA) are severe congenital immunodeficiencies with X-linked inheritance. Although rare, they are all associated with severe infections from early in life, and high morbidity and mortality. Female carriers of these diseases can be identified by a non-random pattern of X-chromosomal inactivation in cell lineages targeted by each gene defect. For patients with WAS, SCIDX1 or XLA, the demonstration of non random X-Chromosome inactivation in their mothers can be used to confirm clinical diagnosis. Furthermore, analysis of X-Chromosome inactivation in at risk females allows preconceptional carrier detection, thus representing an important aid in genetic counseling. For each disease we established a PCR-based, non radioactive assay at the human androgen receptor (HUMARA) locus, that allows analysis of X-Chromosome inactivation in the affected cell types and in tissue specific controls to exclude the issue of skewed X-chromosomal inactivation. In our study, 50 females with a known family history of XLA [19], WAS [18], and SCIDX1 [13],were examined. A carrier status was established in 19 females (7 XLA, 6 WAS, 6 SCIDX1) and excluded in 29 ( 11 XLA, 11 WAS, 7 SCIDX1). Only in 2 cases (4%) the assay was not informative.

Monozygotic twins discordant for Aicardi syndrome

Aicardi syndrome is a developmental disorder characterised by agenesis of the corpus callosum, retinal lacunae, seizures, and developmental delay. It is believed to be X linked with lethality in males. We report a set of monozygotic female twins one of whom is healthy and intellectually normal while the other has the classical Aicardi phenotype with profound retardation. Family history is negative. Both had normal karyotypes. Monozygosity was established by blood grouping, chromosomal heteromorphisms, and DNA analysis using six hypervariable probes (five autosomal and one X linked) and three X linked RFLP probes. We tested the hypothesis that preferential inactivation of a different X chromosome had occurred in each girl. Methylation sensitive RFLP analysis of DNA from EBV transformed B lymphocytes and cultured skin fibroblasts using MspI/HpaII digestion and probing with M27 beta showed a very similar pattern of X inactivation in both twins with no evidence of preferential expression of one particular X chromosome. We conclude that the abnormalities in the affected twin are probably the consequence of a postzygotic mutation in early embryonic development.

Clonality of basal cell carcinoma--molecular analysis of an interesting case

Tumor cells represent a single clone of cells that have undergone a series of mutations in genomic DNA. This process, known as clonal evolution, is a distinguishing feature of cancer. The human androgen receptor gene (HUMARA; GenBank) contains a highly polymorphic cytosine-adenine-guanine trinucleotide repeat that can be used to determine clonality by depicting X chromosome inactivation patterns. Random X chromosome inactivation is consistent with polyclonality; nonrandom X chromosome inactivation indicates a clonal population of cells. Basal cell carcinoma (BCC) demonstrates an atypical growth pattern in that it grows slowly, rarely metastasizes, and is rarely lethal. Whether this tumor results from the accumulation of mutations in a single cell with subsequent clonal expansion or reflects a polyclonal response by a group of cells to a growth stimulus is unknown. To provide further insight into the molecular events characterizing BCCs, we determined the clonal origin of five modular BCCs from a female patient by analyzing X chromosome inactivation patterns at the HUMARA locus. All tumors demonstrated a nonrandom pattern of X chromosome inactivation, consistent with monoclonal proliferation. These findings provide strong genetic evidence that sporadic BCCs develop by clonal evolution and support the contention that a series of mutations in a single cell is responsible for the altered growth state seen in these transformed epithelial cells.

Identification of mutations in the Wiskott-Aldrich syndrome gene and characterization of a polymorphic dinucleotide repeat at DXS6940, adjacent to the disease gene

The Wiskott-Aldrich syndrome (WAS) is an X-chromosome-linked recessive disease characterized by eczema, thrombocytopenia, and immunodeficiency. The disease gene has been localized to the proximal short arm of the X chromosome and recently isolated through positional cloning. The function of the encoded protein remains undetermined. In this study we have characterized mutations in 12 unrelated patients to confirm the identity of the disease gene. We have also revised the coding sequence and genomic structure for the WAS gene. To analyze further the transmittance of the disease gene, we have characterized a polymorphic microsatellite at the DXS6940 locus within 30 kb of the gene and demonstrate the inheritance of the affected alleles in families with a history of WAS.

Isolation of a novel gene mutated in Wiskott-Aldrich syndrome

Wiskott-Aldrich syndrome (WAS) is an X-linked recessive immunodeficiency characterized by eczema, thrombocytopenia, and recurrent infections. Linkage studies have placed the gene at Xp11.22-p11.23. We have isolated from this interval a novel gene, WASP, which is expressed in lymphocytes, spleen, and thymus. The gene is not expressed in two unrelated WAS patients, one of whom has a single base deletion that produces a frame shift and premature termination of translation. Two additional patients have been identified with point mutations that change the same arginine residue to either a histidine or a leucine. WASP encodes a 501 amino acid proline-rich protein that is likely to be a key regulator of lymphocyte and platelet function.

Is skewed X inactivation responsible for symptoms in female carriers for adrenoleucodystrophy?

A study of X inactivation in 12 female carriers for adrenoleucodystrophy showed no evidence that skewed patterns are related to clinical manifestation. Other possible mechanisms to explain manifestation in females are considered.

Evidence for defective transmembrane signaling in B cells from patients with Wiskott-Aldrich syndrome

B lymphocytes from patients expressing the X chromosome-linked immune deficiency disorder, Wiskott-Aldrich syndrome (WAS), fail to produce antibodies in response to stimulation with polysaccharides and other type-2 T cell-independent antigens. To investigate whether this abnormality reflects a defect in the signal transduction cascade normally triggered by ligation of surface immunoglobulin (sIg) on B cells, we have examined early signaling events induced by anti-Ig antibody stimulation of EBV B lymphoblastoid cell lines from WAS patients and healthy controls. Despite the expression of comparable levels of sIg and sIgM on WAS and control EBV B cells, WAS cells failed to manifest the increased proliferation in response to anti-Ig treatment observed in the control cell lines. WAS and control EBV B cells also differed in the magnitude of the change in cytosolic free calcium ([Ca2+]i) induced by sIg ligation; WAS cells showed either markedly diminished or no changes in [Ca2+]i levels whereas control EBV B cells consistently showed increases in [Ca2+]i. Anti-Ig-induced changes in inositol phosphate release were also markedly reduced in WAS compared with control cells. As protein tyrosine phosphorylation is thought to represent a proximal event in the activation of B cells, inducing increases in [Ca2+]i by virtue of tyrosine phosphorylation of phospholipase C (PLC)-gamma, profiles of protein tyrosine phosphorylation and expression of tyrosine-phosphorylated PLC-gamma 1 were compared between WAS and normal EBV B cells before and after sIg cross-linking. These studies revealed that in addition to defective mobilization of Ca2+, the WAS cells manifested little or no increase in tyrosine phosphorylation of PLC-gamma 1 or other intracellular proteins after sIg ligation. Together these results indicate the association of WAS with a defect in the coupling of sIg to signal transduction pathways considered prerequisite for B cell activation, likely at the level of tyrosine phosphorylation. The abnormalities observed in these early transmembrane signaling events in WAS EBV B cells may play a role not only in the nonresponsiveness of WAS patient B cells to certain T independent antigens, but also in the genesis of some of the other cellular deficits exhibited by these patients.

Wiskott-Aldrich syndrome: new molecular and biochemical insights

The Wiskott-Aldrich syndrome is an uncommon X-linked recessive disease characterized by eczema, thrombocytopenia, and immunodeficiency. The clinical features begin early in life and include recurrent infections, bleeding, and severe eczema. Unless the condition is treated by bone marrow transplantation, the prognosis of Wiskott-Aldrich syndrome is grave, and premature death caused by sepsis, hemorrhage, or lymphoreticular malignancy is common. Although the biochemical defect responsible for the syndrome is not known, recent investigations with restriction fragment length polymorphisms have mapped the Wiskott-Aldrich syndrome locus to the proximal portion of the short arm of the human X chromosome (Xp11). The isolation of these DNA markers makes feasible both carrier detection and prenatal diagnosis of Wiskott-Aldrich syndrome and provides an important adjunct to the management of Wiskott-Aldrich syndrome for patients and their families. These genetic data, in conjunction with the recent identification of a specific O-glycosylation defect in lymphocytes from patients with Wiskott-Aldrich syndrome, present an opportunity for the eventual isolation of the Wiskott-Aldrich syndrome gene and identification of the underlying cellular defect. We review the clinical and laboratory features of this syndrome and summarize the new molecular and biochemical approaches that can be used in diagnosis, genetic counseling, and treatment.

Carrier detection in agammaglobulinemia by X chromosome inactivation analysis

Using a recently developed strategy to analyze patterns of X chromosome inactivation in cell populations, we found that two mothers and a sister were carriers in three atypical or sporadic cases of patients with agammaglobulinemia, two of whom were brothers. In this study, a phosphoglycerate kinase 1 (PGK1) gene probe was used to detect patterns of methylation of X-chromosome genes. A random pattern of X inactivation was observed in isolated peripheral blood granulocytes. In contrast, one of the two X chromosomes was preferentially active in the Epstein-Barr virus (EBV)-transformed peripheral B cells of the family members of these patients. The volume of the blood specimen could be significantly reduced using EBV-transformed B cell lines which contained multiple clones. The analysis described here can be used to distinguish between X-linked agammaglobulinemia (XLA) and other forms of a- or hypo-gammaglobulinemia as well as to detect the carrier state.

Defective B-cell and regulatory T-cell function in Wiskott-Aldrich syndrome

We report two Chinese boys with Wiskott-Aldrich syndrome presenting with gastro-intestinal bleeding, eczema and recurrent infection. They had thrombocytopenia and the mean platelet volume was small. Serum IgG and IgA were elevated and lymphocyte proliferation in response to phytohaemagglutinin, concanavalin A and pokeweed mitogen was defective. Despite documented herpes simplex virus type 1 and cytomegalovirus infection in one patient, he did not mount any humoral response. The generation of antibody-secreting cells in response to pokeweed mitogen was markedly defective in a plaque-forming cell assay. Both patients' regulatory T-cell and B-cell functions were defective in this assay. The genetic defect in Wiskott-Aldrich syndrome therefore affects T-cells, B-cells and platelets.

X inactivation as a mechanism of selection against lethal alleles: further investigation of incontinentia pigmenti and X linked lymphoproliferative disease

Thirty-one females with incontinentia pigmenti (IP), 42 controls, and 11 females from four families segregating for X linked lymphoproliferative disease (XLP) were studied for evidence of skewed X inactivation by analysis of methylation at sites in the HPRT, PGK, and M27 beta (DXS255) regions of the X chromosome. Extensive skewing of X inactivation was present in blood from 4/42 (9.5%) control females and 11/31 (35%) of those with IP. This frequency of skewed inactivation was seen in both familial and sporadic cases of IP. Analysis of inactivation in mother/daughter pairs, both affected and control subjects, showed no familial consistency of pattern, arguing against specific mutations being associated with particular patterns of inactivation. In the only informative family where both mother and daughter were affected by IP and showed skewed inactivation, the IP mutation was on the active X chromosome. This argues against cell selection during early embryogenesis being the explanation for the skewed inactivation observed. These data confirm that skewed inactivation of one X is observed in lymphocytes from a significant minority of normal females, and is seen with raised frequency in IP heterozygotes. It is not, however, a universally observed phenomenon, and the relationship of X inactivity to the IP mutation appears to be complex. In the case of XLP, though skewed X inactivation patterns are seen in most disease carriers, the frequency with which this phenomenon occurs in normal females renders it an unreliable diagnostic marker for XLP carriers.

Genetic study of a new X-linked recessive immunodeficiency syndrome

Seven forms of X-linked (XL) immunodeficiency have been described (XL agammaglobulinemia, XL severe combined immunodeficiency [SCID], Wiskott-Aldrich syndrome, XL chronic granulomatous disease, XL hyper-IgM syndrome with low IgG and IgA, and XL lymphoproliferative syndrome), and properdine deficiency. Although there are (some) phenotypic variants, diagnosis is relatively simple on the basis of clinical, immunological, and genetic characteristics. We studied a family in which several males were affected by severe infections and whose pedigree suggested recessive XL inheritance of an immunodeficiency. Immunologic and genetic studies (X inactivation patterns in females and restriction fragment length polymorphism [RFLP] segregation) were performed in order to characterize the immunodeficiency. The propositus, a 5-yr-old boy, was found to have a severe and progressive T- and B-cell functional immunodeficiency characterized by defective antigen-specific responses. No lymphocyte subsets or membrane anomalies were detected and the immunodeficiency did not correspond to usual XL forms. Studies of DNA from two of the informative females, the mother and one sister revealed nonrandom X chromosome inactivation of T cells and, partially, B cells but not PMN, a pattern similar to that observed in XL SCID carriers. RFLP studies identified a haplotype segregating with the abnormal locus that may be localized in the proximal part of the long arm of the X chromosome. We thus report the characterization of a new XL immunodeficiency that may correspond either to another XL locus or to an attenuated phenotype of XL SCID.

The molecular basis of X-linked immunodeficiency disease

The molecular bases of the X-linked immunodeficiency diseases remain largely undetermined. Two of the genes involved in these diseases have been isolated, namely the genes for X-linked chronic granulomatous disease and properdin deficiency, and substantial progress has now been made in identifying the genes which are defective in the other five diseases, Wiskott-Aldrich syndrome, X-linked severe combined immunodeficiency, X-linked agammaglobulinaemia, X-linked hyper-IgM and X-linked lymphoproliferative syndrome. We review here the nature of the diseases, progress made in identifying and isolating the genes involved and the prospects for improved prenatal detection, carrier status determination and treatment of these life-threatening conditions.

False-negative prenatal exclusion of Wiskott-Aldrich syndrome by measurement of fetal platelet count and size

The study of the fetal platelet count and size can, according to the literature, be used for the prenatal diagnosis of the Wiskott-Aldrich syndrome (WAS). So far, no affected fetuses have been identified by this method. All pregnancies in which this method had been applied to resulted, as correctly predicted, in the birth of normal children. Here we report on a familial case of WAS where the haematological parameters failed to reveal the affected second child. Hence we assume that the platelet count and size of platelets remain normal in fetuses with WAS to the gestational age of 22 weeks and cannot be used for prenatal diagnosis.

The gene encoding human TFE3, a transcription factor that binds the immunoglobulin heavy-chain enhancer, maps to Xp11.22

TFE3, a member of the helix-loop-helix family of transcription factors, binds to the microE3 motif of the immunoglobulin heavy-chain enhancer and is expressed in many cell types. We have localized human TFE3 to the proximal short arm of the X chromosome using a somatic cell hybrid panel. A frequent RsaI RFLP detected by the TFE3 cDNA was found and used to confirm this location by linkage analysis in 20 pedigrees. Two-point and multipoint lod scores place TFE3 near markers in Xp11.22 with the most likely order DXS7-DXS255-TFE3-DXS146-DXS14.

Molecular analysis of X-linked agammaglobulinemia with growth hormone deficiency

To address the relationship between the gene (or genes) that causes the syndrome of X-linked hypogammaglobulinemia with isolated growth hormone deficiency and the gene responsible for typical X-linked agammaglobulinemia (XLA), we have used cytogenetics, examination of X chromosome inactivation patterns in potential carriers of the defect, and linkage analysis to study two unrelated families in which the affected males had isolated growth hormone deficiency and immunologic findings indistinguishable from those of typical XLA. A deletion could not be demonstrated in either family by G-banded karyotypes or flow cytometric analysis of metaphase chromosomes. Studies of X inactivation showed that mothers of affected boys from both families exhibited selective use of a single X chromosome as the active X chromosome in B cells but not T cells. This pattern is the same as that seen in obligate carriers of typical XLA. Linkage analysis demonstrated the most likely location for this gene (or genes) to be the midportion of the long arm of the X chromosome between DXS3 and DXS94. This segment of the X chromosome, which constitutes approximately 5% of the total X chromosome, encompasses the gene for XLA. These findings are consistent with the combination of XLA and growth hormone deficiency being caused by a small, contiguous, gene deletion syndrome involving the gene for XLA or an allelic variant of the gene for typical XLA.